In models of inelastic DM, the dark sector comprises two states \(\chi _1\)  and \(\chi _2\)  with a mass splitting \(\delta =M_{\chi _2}-M_{\chi _1}\) . At tree level, \(\chi _2\)  couples to \(\chi _1\)  via a scalar or a gauge boson field, but the self-coupling \(\bar{\chi }_1\chi _1\)  or \(\bar{\chi }_2\chi _2\)  is loop-suppressed. In the simplest case, we consider the Lagrangian \(\mathcal {L}\supset g\phi \bar{\chi }_2\chi _1+h.c.\) . Since \(\chi _2\)  is heavier than \(\chi _1\) , after freeze-out we expect \(\chi _2\)  to be depleted either though decay or through the interconversion process \(\chi _2\chi _2\rightarrow \chi _1\chi _1\)  when the temperature of the universe falls below the mass splitting, \(T<\delta \)  [1]}, [2]}. As a consequence, the dark matter today is dominated by \(\chi _1\) .
